The present invention relates to an image reproduction system such as a printer or a copier and particularly to the transfuse member which is part of such a system and is intended for transfusing toner on the receptor material.
In a typical image reproduction system such as a printing or a copying system, a latent image is formed on an image-forming member by image-wise exposure using a known graphical process. The image-forming member can be an endless member such as a drum or a belt. Typical graphical processes include amongst others magnetography, ionography, and electrography, particularly electrophotography. At present electrophotography is the most widespread. In the latter process, a charged latent image is formed on a pre-charged photosensitive member by image-wise exposure to light. The latent image is subsequently made visible on the image-forming member with charged toner at a development zone. After the development of the latent image, the developed toner image is transferred directly or via one or more intermediate transfer members to a receptor material. The receptor material can be in the form of a web or in sheet form. In the latter case, the receptor material is preferably carried on a conveyor. In general however, to enable the ability to print on a wide range of receptor materials without having to go first through an elaborate medium qualification procedure and thereafter through a demanding medium conditioning procedure, intermediate transfer members are introduced. These intermediate transfer members are usually in the form of endless belts or drums. Furthermore, where in a system without intermediate transfer members the images are first transferred to the receptor material and thereafter fused using non-contact fusing, e.g. using radiant heating, or contact fusing. In contact fusing a nip zone is usually created between the receptor material and a heated member by pressure. In this nip zone the toner images are fused to the receptor material by pressure and heating to temperatures well above 150 degrees Centigrade, usually above 170 degrees Centigrade. In systems having at least one intermediate transfer member, one can opt to simultaneously transfer and fuse the toner images to the receptor material. This principle is hereinafter referred to as transfuse, while the intermediate transfer member in contact with the receptor material is referred to as the transfuse member. The contact zone between the transfuse member and the receptor material is hereinafter referred to as the final transfer zone. A typical example of such a system is disclosed in U.S. Pat. No. 6,047,156. In a multi-color reproduction system the configuration is such that in operation the heated transfuse member carries a registered composite multi-color toner image which is subsequently transfused to the receptor material in the final transfer zone.
There are two general approaches known in the art to facilitate the transfer, more particularly the release, of the composite multi-toner image from the heated transfuse member to the receptor material. In a first approach, use is made of a release agent metering system such a system is described in EP 09977944A1, EP 0997795A3, and EP 1004944A1 (Xeikon N.V.) which are hereby incorporated by reference in order to apply typical amounts of a release agent, e.g. silicone oil, on the outermost layer of the transfuse member. In another approach, use is made of an outermost layer where the release agent is inherent or built-in, such as certain silicone layers. Particularly silicone layers with a high swelling factor are preferred as the inherent or built-in release agent in such layers can easily migrate to the outermost surface. Such a layer is e.g. described in EP1014220 (Xeikon N.V.) which is hereby incorporated by reference. Optionally, a top coating is provided on such a layer with inherent or built-in release agent provided that this top coating is permeable for this release agent. In both approaches an amount of release agent is applied to the outermost surface of the transfuse member corresponding to an amount of at least 10 mg release agent per printed A4 side of receptor material. Although the introduction of a release agent on the outermost surface of the transfuse member, according to the afore-mentioned approaches, can be beneficial for the release, it has been determined experimentally that the presence of such amounts of release agents on the transfuse member is detrimental for the print quality due to back propagation of this release agent to the photosensitive element, directly or via one or more intermediate transfer members.
One aspect of the invention includes a transfusing member that can be used in hot-pressure fixing of toner particles to a substrate while avoiding the use of substantial amounts of release agents on the surface of the transfuse member.
Another aspect of the invention includes an outermost layer for the transfuse member and a toner composition associated therewith that combine good hot offset properties with low temperature fixability, particularly for temperatures in the range from 80 to 140 degrees Centigrade.
The present invention is particularly relevant to printers and copiers where, to enable printing on a wide variety of receptor materials, at least one intermediate transfer member is provided to transfer a developed toner image from an image forming station to a receptor material. The intermediate transfer member contacting the receptor material constitutes the transfuse member referred to herein. The transfer of the developed toner image from the transfuse member to the receptor material and the simultaneous fixing thereof, hereinafter referred to as transfuse, is by means of heat and pressure. In particular, the transfuse member may be in the form of a belt or drum heated to a temperature typically in the range from 80 to 140 degrees Centigrade. The surface of the transfuse member carrying the unfixed composite toner image contacts one face of the receptor material in the final transfer nip where the toner image is transfused. In case the transfuse member is in the form of a belt, this final transfer nip may be created by feeding the heated transfuse member and the recording material simultaneously between a first guide roller contacting the back of the heated transfuse member and a second guide roller contacting the back of the receptor material while pressure is exerted on at least one of these guide rollers to define the contact. Alternately, in case the transfuse member is in the form of a drum, the final transfer nip may e.g. be created by feeding the recording material between the transfuse drum and a counter roller contacting the back of the receptor material while pressure is exerted on the drum and/or the counter roller to define the contact.
According to the present invention, a fixing device for fixing toner images onto a receptor material is disclosed comprising:
an endless transfuse member urged into contact with an endless backing member to form a final transfer zone there-between through which a receptor material path extends, said endless transfuse member having an outermost layer of a material selected from the group of polyorganosiloxanes, fluorosilicones, phenylsilicones, fluoro-elastomers, and mixtures or hybrid compositions thereof, said outermost layer having a peel force, being measured according to Finat No 3, with tape TESA 4163 at a peeling speed of 30 cm/min, above 7 N/m or from 25 N/m to 200 N/m, or from 40 to 140 N/m or from 20 N/m to 100 N/m or from 40 N/m to 100 N/m; and
at least one heating device for heating said endless transfuse member to a temperature from 80 to 140 degrees Centigrade.
The fixing device may further comprise a release agent metering system contacting said outermost layer of said transfuse member for applying an amount of release agent on the outermost surface of said outermost layer corresponding to an amount of 0.5 mg per side A4 of paper or below. The release agent can be a silicone oil or more preferably a functional oil can be used as e.g. disclosed in U.S. Pat. No. 5,576,818.
Further according to the present invention, a method is disclosed for fixing unfixed toner images on a receptor material, comprising the steps of:
heating unfixed toner images on an endless transfuse member to a temperature from 80 to 140 degrees Centigrade, said transfuse member having an outermost layer of a material selected from the group of polyorganosiloxanes, fluorosilicones, fluoro-elastomers, phenylsilicones, and mixtures or hybrid compositions thereof, said outermost layer releasing an amount of release agent corresponding to an amount of release agent of 0.05 mg per printed side of A4 paper or below, measured on NopaColor 100 gsm paper at an operating temperature for the transfuse member of 120 degrees Centigrade; and
transfusing said heated toner images to a surface of a receptor material by urging said endless transfuse member against an endless counter member while said receptor material is fed there-between. Preferably, the outermost layer has a peel force, being measured according to Finat No. 3, with tape TESA 4163 at a peeling speed of 30 cm/min, above 7 N/m.
Preferably the transfuse member is heated internally, e.g. by using at least one heating roller or at least one heating lamp. Additionally or alternatively, a radiant heating device may be provided to heat the composite toner image on the transfuse member in advance of the final transfer zone. It may be advantageous to heat the transfuse member to a uniform temperature. By a uniform temperature a maximum temperature drop of 30% during one cycle of the transfuse member is meant. The composite toner image may be formed of toner particles from a dry or a liquid developer. In the latter case the developed toner images may be compacted before being transferred to the transfuse member.
In an embodiment of the invention the outermost layer of the transfuse member is a polyorganosiloxane or a fluorosilicone with a swelling factor SF of 2 or below, preferably 1.5 or below, and more preferably 1.3 or below.
In another embodiment of the invention the outermost layer of the transfuse member is a phenylsilicone, or a fluoro-elastomer, or a fluorocarbon with a swelling factor SF of 1.3 or below.
In another embodiment of the invention, the transfuse member carries a multi-color composite toner image in advance of the final transfer zone. A color is defined as a pigment such as e.g. cyan, magenta, yellow, red, green, blue and includes black. The toner particles of said composite toner image have a Storage modulus, Gxe2x80x2 from 5000 to 15000 Pa when measured at a temperature of 125 degrees Centigrade and a frequency of 16 Hz. More preferably, the toner particles have a melt viscosity from 10 to 500 Pa s measured at 100 rad/s at 120 Centigrade degrees.
In a further embodiment of the invention, unfixed toner particles in image form are carried on the transfuse member and are transferred to the receiving material and fixed thereon as the receiving material passes through the final transfer zone. The unfixed toner particles may be deposited upon the transfuse member by any means known in the art, such as described in U.S. Pat. No. 5,805,967 (De Bock et al./Xeikon NV) which is hereby incorporated by reference.
In case the transfuse member is a belt, this belt preferably comprises an electrically conductive backing member covered with the outermost layer according to the present invention. Alternatively at least one layer may be provided between said backing member and said outermost layer particularly for reasons of conformability. This layer can be composed of e.g. a silicone elastomer, polytetrafluoroethylene, fluorosilicones, polyfluoralkylene or other fluorinated polymers. This layer may be doped with electrical or thermal conductive fillers. The total thickness of the transfuse member may range between 0.15 and 1.5 mm, or for reasons of conformability between 0.4 and 1.5 mm.
The electrically conductive backing member may be composed of a metal such as e.g. stainless steel. Alternatively, an optionally reinforced or pre-stressed fabric backing member may be used.
The receptor material can be in web form or in sheet form. In the latter case, the receptor material is preferably transported on a conveyor. Typical receptor materials are papers, films, label stock, cardboard etc.